I would do 2 cp3s. If anything i would only do some mild porting with the heads. I had a set ported quite a bit last year, and they only lasted 1 pull before cracking. Duramax heads are hard to port, so i ran a spare set last year that was ported very mildly, and didnt match my intake. This year i just had them all matched and called it good. So mild porting and valve springs is the only thing i would do, i think out of all the head work, valve springs is the only gain you will notice. But like i said, i would do cp3s first if your big pump wont keep up.